The Aeoline is a string stop of very soft tone;
the softest string tone in the organ, according to Audsley
(but see Echo Aeoline).
It is usually found at 8' pitch, but 4' and 16' examples are sometimes found.
As a flue stop it first appeared around 1820 in Germany,
and soon became popular in Germany, Switzerland and America
in both large and small instruments.
The names Aeolina, Aeoline and Äoline
have also been used for a reed stop; see
Aeoline Reed.
Irwin gives a different definition for Aeolina

Different sources variously describe the Aeoline as
belonging to the Gamba,
Salicional, or
Viol family.
The degree of “stringiness” varies between different examples,
being more stringy in German examples, according to Maclean.
Audsley considers it an Echo Salicional or,
if voiced with a more stringy tone, an Echo Viola da Gamba.
Bonavia-Hunt and Wedgwood mention Echo Salicional without
reference to the Aeoline, but without any description whatsoever.
In the absence of further information, we consider them to be synonyms.
According to Maclean, Casavant sometimes used the name
Dolcissimo for their Aeolines.

The Aeoline is often used as one rank of a
celeste.
Audsley and Locher claim that it is often used with
the Voix Celeste,
though that stop is usually intended for use with the louder
Salicional.

Construction

The Aeoline is constructed of small scale cylindrical metal pipes,
sometimes slotted. Audsley prefers tin or Hoyt metal.
The widths of the mouths are from 1/5 to 2/9 the circumference,
with very low and sharp cut-ups.
Each mouth is fitted with a roller-bridge or a small adjustable
curved beard, as shown in Audsley's drawing which is reproduced
here, which Audsley says “greatly aids the production of the delicate
string-tone which is the desirable characteristic of the stop.”
He specifies a wind pressure of 1.5" to 2.5".
The lowest octave is sometimes made of wood, and sometimes stopped,
and in cases of limited space or funds, may be borrowed from another
stop.
These latter practices cannot be recommended, as it is impossible
to obtain string tone from a stopped pipe (unless it is
Haskelled).
There is considerable variation in scales given in the literature:

Source

8' C

4' C

2' C

1' C

Ratio

Wedgwood

3.5"

Audsley

2.51"

1.54"

0.94"

1:2.519

Bonavia-Hunt

2 1/2"

1 1/2"

Bonavia-Hunt

2"

1 1/4"

3/4"

15/32"

halve on 20

Bonavia-Hunt

1 1/2"

1"

5/8"

7/16"

halve on 24

Bonavia-Hunt

1 1/8"

13/16"

9/16"

11/32"

halve on 24

Variants

Examples

Osiris contains about 100 examples of Aeoline, and eight
of Aeolina.
All known examples of the other names (as flue stops) are given below.
No examples of Echo Viola da Gamba are known.
Contributions welcome.

Aeoline 8', Manual II; Basilika Maria-Treu, Vienna, Austria;
Buckow 1858. This is the oldest known example of this name used as a flue.